Means for preventing electrical interference



S. l. CORY MEANS FOR PREVENTING ELECTRICAL INTERFERENCE Filed May 6,1922 u G BOOO a IN VEN TOR. J. Z '60! ATTORNEY Patented Apr. 28, 1925.

'umreosrares earner series.

SAMUEL I. CORY, OF ELMHURST, NEW YORK, ASSIGNOR 'lO AMERICAN TELEPHONEAND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MEANS FOR PREVENTING ELECTRICAL INTERFERENCE.

Application filed May 6,

To all whom it may concern.

Be it known that I, SAMUEL I. Corr, residing at Elmhurst, in the countyof Queens and State of New York, have invented certain Improvements inMeans for Preventing Electrical Interference, of which the following isa specification.

This invention relates broadly to means for protecting circuits fromexternal interference, and more particularly to an arrangement forreducing or preventing crossfire in a system of grounded telegraphcircuits. v

In the operation of grounded telegraph circuits in which signals aretransmitted by means of impulses of opposite polarity, interferingimpulses are set up in adjacent circuits to that over which the signalsare being transmitted by virtue of the mutual admittance between thevarious circuits of the system. 'These interfering impulses, which arecreated in the exposed circuits, fiow to ground at each end of theexposed circuits in proportion to the magnitude of the impedances. Theeffect of the interfering mpulses thatflow through. the distantreceiving apparatus of the exposed circuits is termed the receiving-endcross-fire, and the effect that the interfering current produces in thereceiving apparatus in the exposed circuits at the near, or home, end ofthe exposed circuits, is known as sending-end crossfire. v

In my copend-ing application, Serial No.

533,370, filed February 1, 1922, I have shown an arrangement whereby, ina duplex tele graph system, the receiving end cross-fire in the exposed.circuits is prevented orgreatly reduoedby an inductive coupling betweenthe disturbing and the disturbed circuits. In the system thereindisclosed, the transmission of a signaling impulse over one circuitiwillproduce in the disturbed circuit not only an interfering impulse butalso a neutralizing impulse, which is adapted to oppose andneutralizethe interferingimpulse that would tend. to pass through thedistant receiving apparatus and 'cause a disturbance therein.

In such system, the sending-endcross-fire is prevented by means ofcondensers connected between the artificial lines of the disturbing anddisturbed circuits so that by means of this combination of devices, boththe receiving-end. andsending-end crossfire, is prevented. Aninductivecoupling of the type 1922. Serial No. 559,010.

shown in the said copending application would tend to neutralize thereceiving-end cross-fire 111 single-line Morse circuits, but, at

the same time it would tend to increase the sending-end cross-fire insuch circuits.

Itis the object of this invention to provide an inductive arrangementfor neutralizing both the receiving-end and the sending-end cross-fire1n single-line Morse circuits.

This invention will be better understood from the following descriptionwhen read in connection with the attached drawing, which shows one formof embodiment of the inven tion.

source of potential 8, (which is of opposite polarity to the source 4) acurrent-limiting resistance 9 and a line relay 10. The terminal circuitof line 1 at A includes a winding 13 of the neutralizing transformer 11,in series with the said line and a winding 14 of the said transformer,which is connected in a branch circuit to ground, the said branchcircuit including in addition to the winding 1%, a condenser 42'and aresistance 13. similarly, at station E, the terminal circuit of the line1 includes a series winding 15 of the transformer 12 and another winding16, which is connected in a branch circuit to ground, the said circuitincluding in addition to the winding 16 a condenser 48 and a resistance4.9. The transformers 11 and 12 serve to linkinductively the linecircuits l and 2. These circuits are also linked together by means ofthe transformers 23 and 24, of which the windings 25 and 27,respectively, are connected in series in the line 1, and the windings 26and 28 respectively in series with the line 2. The windings oftransformers 23 and 24 are so arranged that the flow of current in adefinite direction in one of said windings will produce a flow ofcurrent in the opposite direction in the other winding of the saidtransformer. Theline 1 is connected with the terminal circuits bymeansof the composite sets 17 and 18, the former of which comprises aseries induc- 3, a grounded tance 19 and a shunt capacity 20, and thelatter a series inductance 21 and a shunt capacity 22.

The line circuit 2 has connected there'- with at station A a key 30, abattery 31, and a resistance 32 and line relay 33, and similarly atstation E a key 34, a battery 35, of opposite polarity to battery 31, aresistance 36 and a line relay 37. Furthermore, at station A theterminalcircuit has connected therewith a series winding 38 ot the transformer11, and a shunt winding 39, which is'in a branch circuit to ground,including the condenser 4 1 and resistance lfi. Similarly at station Bthe terminal circuit includes a series winding so of the transformer 12and a shunt winding d1, which is in the branch circuit to ground,including the condenser at; and the resistance 41-7 The line circuit 2is connected to its respective terminal circuits by means of thecomposite sets 50 and 51, which comprise the series i11- ductances 52and 5% respectively and the shunt condensers 53 and respectively.

The manner'm which the recen lng-end and the sending-end crossfire maybe re- ,duced or prevented will be clear from the following descriptionof what occurs when signals are transmitted over the line 1 from thestation A to station B, while the line circuit 2 is idle. For suchconditions, key 7' of the line 1 at station B will remain closed and thekey 3 at station A will be operated for the transmission of signals.Keys 30 and 34, connected with the line 2, will remain closed, which isthe normal position of such keys when a circuit of this type is idle.vLet it be assumed that. key 3 has just been closed for the transmissionof a markingsignal over the line 1. Current will flow along the line 1in the direction represented by the solid arrows. This current will flowthrough the windings 13 and 25 and 27 and 15 in series. Current willalso How through the winding 14 of the transformer 11 to ground in thedirection shown by the solid arrow, and likewise will flow through the'winding 16 of the transformer 12 to ground. The magnitude of the currentflowing, for example, through the winding'l to groruid may be varied byadjusting the condenser 42 and the resistance 43 in series with the saidwindin and con sequently. this current may be made greater or less thanthe current flowing through the winding 13. S nce these wlndnigs are inparallel opposition the flux produced by the respective currents will bein opposition so that it the currents are unequal, a resultant flux ineither one directlon or the other will occur, depending upon thewindwinding 14:, so that the resultant flux will be shown by the crossedarrow within the core of the transformer. This flux will induce in thewindings 38 and 39 a difference of potential such as to cause a flow ofcurrent in the said WlIICl'lDgS in the direction represented by thedotted arrows. A similar result will occur in connection with thetransformer 12, wherein a resultant flux, as represented by the crossedarrow, will produce in the windings 10 and 41 a difference of potentialsuch as to cause a current flow in the direction represented by thedotted arrows. The flow of current through the windings 25 and 27 of thetransformers 23 and 24 will produce a flow of current in dotted arrow,in the windings 26 and 28.

The transmission of the signaling impulse over the; line 1 will producean interfering current in the line 2, which will flow therein in thedirections represented by the wavy arrows toward the grounds at theterminals of the said line. The flow of interfering current toward theterminal B of line 2 will be substantially eliminated by the flow ofcurrent in opposite direction, as shown by the dotted arrows, whichthereby prevents the said interfering current from producing any effectupon the receiving relay 37, connected with the disturbed circuit at thestation B. Since, however, the interfering current and the neutralizingcurrent are flowing in the same direction toward the station A, agreater effect would be produced, upon the receiving relay 33 than it noneutralization had been attempted, were it not for the presence of theneutralizing transformer 11 which is designed to afford protection forthe sending-end receiving apparatus. As has been stated heretofore, theproduction of a resultant .flux in the transformer core, as representedby the the neutralizing current produced by the transformers 23 and 24,and also opposite in direction to the interfering current'flowing fromthe line 2 towards the terminal A. By the proper adjustment of thecondenser a l and theresistance 45 the magnitude oi the current flowingin the circuit just traced may be proportioned so as to eflectthe entireneutralization of the interfering current and of the neutralizingcurrent that flowspin the direction from the line .2 towards the groundat the terminal A.

It will be seen, therefore, that by means of the arrangement shown inthe attached receiving-end cross-fire and the sending-end be entirelyeffected.

lVhereas this invention has been shown applied to a system embracingonly two circuits, it is to be understood that it is not so limited,since it may be applied to a system embracing any greater number ofcircuits; and, as applied, it will function in the same manner as itdoes in the system heretofore described and shown.

Furthermore, although this invention has been disclosed as embodied in aparticular form and arrangement of parts it is to be understood that itis not thus limited but is capable of embodiment in other and differentforms without departing from the spirit and scope of the appendedclaims.

What is claimed is:

1. In a single-line Morse telegraph system, the combination with aplurality of line circuits of terminal circuits connected with each endof the said line circuits, and a multi-winding transformer havingwindings connected in series with the said line circuits and alsowindings connected between each of said line circuits and ground forneutralizing interfering currents of the said line circuits.

2. In a single-line Morse telegraph system, the combination with aplurality of single-line Morse telegraph circuits of a multiwindingtransformer having groups of windings connected therewith, each groupbeing connected with a line circuit in such manner that one winding of agroup will be in series with its line circuit and the other winding inshunt to ground.

In a single-line Morse telegraph system, the combination with aplurality of line circuits, each having terminal apparatus cross-fire ingrounded telegraph circuits may connected therewith, of a transformerhaving groups of windings connected therewith, one winding of each groupbeing connected in series with a line circuit and the other winding ofeach group being connected in shunt to ground, the circuits of the saidwindings being so arranged that the flux resulting from the transmissionof a signaling impulse over one of said line circuits will create in theother windings of the other group an elect-romotive force such as toneutralize interfering cross-fire set up in the other circuit connectedwith the said latter group of windings.

4. I11 a single line Morse telegraph system, the combination with aplurality of line circuits, of terminal circuits connected with each endof the said line circuits, a multi-winding transformer having windingsconnected in series with each of said line circuits and also havingwindings connected. between each of the said line circuits and ground,and a second transformer having a plurality of windings each individualto and connected in series with one of the said line circuits wherebythe receiving-end and the sending-end crossfire may be substantiallyneutralized.

5. In a single line Morse telegraph system the combination with aplurality of single line Morse telegraph circuits of a multiwindingtransformer having groups of windings connected therewith, each groupbeing connected with a line circuit in such manner that one winding of agroup is in series with its line circuit and the other winding in shuntto ground, and a second transformer having a plurality of windings eachindividual to and connected in series with one of said line circuitswhereby the receiving-end and the sending-end crossfire may besubstantially neutralized.

In testimony whereof, I have signed my name to this specification this5th day of May, 1922.

SAMUEL I. CORY.

